Method of enriching iron ore, blast furnace flue dust, burnt pyrite, purple ore and the like



Patented Dec. 10, 19229 uNrrso STATES smear rains 7 HENRY AUGUST MUELLER, OF STO(fl'flzlOLIlVlI, SWEDEN, ASEJGNOR T0 AKTIEBOIJAGET TEERRICONCENTRAT, OF STOCKHOLM, SWEDEN METHOD or nnmcnme IRON can, BnAs'r rcnnacn FLUE nus-"r, BURNT rvnrrn,

PURPLE one AND THE LIKE V 1T0 Drawing. Application filed August 22, 1927, Serial No. 214,778, and in Sweden October 28, 1926.

Certain iron-ores are, as well known, in their natural state only feebly paramagnetic so that they either notat all or only by use of high intensity magnetic separators can be i 6 enriched in the magnetic way. To this class 10 burnt pyrites belong the iron ores of the types Fe 3 (brown and red hematites, iron-glances etc.) FeO CO (spathic ores etc.) and hydrate ores. This is also true of blast furnace fluedust,

and purple-ore, which essentially consist of ferric oxide (Fe O As the magnetic separation of such ores by means of high intensity magnetic separators is very expensive and often gives a bad result, magnetic methods have heretofore not been generally used for their enrichment, or they have been transferred by partial reduction with carbon ,(spathic ores being first heated and oxidized to F'e 'O and then partially reduced) more or less completely to ferrosoferric oxide (FegOQ so as to renderthem sufficiently paramagnetic to be separated in low intensity magnetic separators. It has been proved by experience that in the latter case at least half of the ore must be transferred into ferroso-ferric oxide to obtain a ferred by heating into a highly paramagnetic ferric oxide. 7 g

It is sufficient for obtaining this effect to heat the ferric oxide or the ferric oxide ore to a comparatively moderate temperate about 600 C.) and during a short time i about Q to A hour) The heating is, preferably, effected in an indirect way. It has been found that the best results are obtained, if the heating of the ferric oxide takes place in presence of a small amount of carbonaceous 'gle operation.

material in solid, liquid or gaseous state (for I instance by Weight of coal powder). The cooling of the heated material can also be made in the air without any change of the high paramagnetism obtained taking place. That the result achieved by the present method is not due to any chemical change is evident both fromv the chemic'alanalysis which gives an essentially unchanged chemical composition and from'spectro-graphic investiga tions, which show that-the treated material has still the rhombic crystal form of theferric oxide, A minetteore treated according to the invention was found at the analysis to contain 78.10% F6203 and only 2.06% E30, another contained 7 6.06% Fe2O and 1.54% F eO. An oolit-ore, which was treatedin the above manner was found at the analysis to contain 7 414% Fe O and only traces of FeO. It was found at the microscopic investigation that the iron mineral had in this last case been re-crystallized in such a way that ironglance had been produced. Thissample was very strongly paramagnetic and hadeven a remnant magnetism after magnetic separation. i

When spathic iron-ore is treated according to this method, presence of air, so that ferric oxide (Fe- 0 is produced.

either separately or in the same operation,

itis first to be calcined in i This ealcination can be effected v which brings forth the paramagnetism of the ferric oxide. In the latter case it should be observed that the last part of the heating process for transferring the oxide produced to paramagnetic ferric oxide should, preferably, beperformed without admission of air.

Hydrate ores are when heated transferred directly to ferric oxide while water is driven off and,therefore, their transferring to paramagnetic ferric oxide can be made in a sin- Blast furnace flue dust contains generally such a large amount of carbon that it is sufficient for reducing all ferric oxide therein to ferrous oxide. lVhen treating such material according to this invention such a short heating time and such a low temperature are to be used, that substantially no reduction takes place and, therefore, if the heating is made without admission of air the carbon is conticles of the material treated. By admitting air in a regulated amount part of the carbon can be combusted to generate some or all of the heat required for the heating. An other way generally more advantageous of utilizing the carbon content of the blast furnace flue dust is to use the flue dust as an addition to other ores not containing carbon in such quantity that the mixture contains about A to 70 by weight of carbon. If the carbonaceous blastfurnace flue dust is added in a larger amount part of the carbon can also in this case be combusted by admission of air to generate the heat necessary for the process. When non-carbonaceous ores are treated without addition of carbonaceous blast furnace fiue dust part of the fuel necessary for the heating is mixed with the ore and combusted by a regulated admission of air.

For the heating any suitable furnace construction can be used. As the temperature required for the treatment is rather low the furnace can bebuilt entirely or partly of iron.

It is generally advantageous to cool the heated ore in air-inorder to transfer the ferroso-ferric oxidewhich may be formed in small quantities, to ferric oxide. If this cooling is carried out according to the countercurrentprinciple and not too rapidly the mineral often is rendered more strongly mag- ;netic than by cooling without admission of air or in water. The air used for cooling the ore and thus preheated can be used for the combustion of the fuel which is required for the heating of the ore or to preheat the ore to be treated whereby a considerable saving of fuel can be obtained.

After transferring of the material to paramagnetic ferric oxide the magnetic separation is effected in common lowintensity magnetic separators. I In the practical use of the "invention ferric oxide materials have been obtained with a stronger paramagnetism than that of ferroso-ferric oxide and the output in separating the materialin a low intensity magnetic separator has reached a 'value of 95 to 97.5%.

What I claim is:

1-. Methodof treating oxide iron ores,

blast furnace flue dust, burnt pyrites, purple ore and the like which in their natural state are only weakly paramagnetic, which comprises heating the material to about 600 C.

substantially in absence of free oxygen while in presence of carbonaceous material in quantity suflicient to bind the free oxygen between the ore particles but insuflicient 'toessentially alter the oxidation stage of the iron mineral, and'then separating the material in a low intensity magnetic separator. v

4. Method oftreatingoxide iron ores and the like, which in their natural stateare only weakly paramagnetic, which comprises mix;-

ing non-carbonaceous:oxide iron ore; with carbonaceous blast furnace flue dust in such quantity that the carbon content of the mix- 7 'ture is sufficient to bind the free oxygen present between the ore particles but insufficient essentially to alter the oxidationst-age of the ore, heating the mixture to about. 600 C.

while excluding the atmospheric air,andfinally separating the material'in a low intensity magnetic separator. .7

In testimony whereof I. have signedmy name. I

HENRY AUGUST MUELLER.

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